Risk Matrix Table:
Neglible
Slight
Moderate
Serious
Very serious
Health and safety: -
No absence from work
Minor first aid required
Injury leading to lost time
Possible permanent disability, possible fatality
Environment: -
No significant impact. Easily controlled on worksite
Short term effect on site, controlled on worksite
Local pollution, may have lasting effect on worksite
Major uncontrolled release Pollution extending beyond extending well beyond worksite. worksite, effects for more than 6 Serious pollution for more than months 12 months
Operations: -
Short or no delay in operations. Minor delay in operations. Minor Operation delayed/Degraded. Trivial asset damage asset damage. Moderate asset damage.
Operational failure. Critical asset damage.
1
2
Severity 3
4
5
1
2
3
4
5
2
4
6
8
10
3
6
9
12
15
4
8
12
16
20
5
10
15
20
25
Low
High
Low
Extremely Improbable
Operational failure. Serious asset damage.
One or more fatalities
1 ' An accident could only occur under freak conditions
Improbable 2
Possible The accident may occur if an additional event takes place.
Probability
An accident might occur if other factors were present but the risk is minimal.
3
Probable 4
The accident could be precipitated by wind, vessel movement, vibration or human carelessness.
If work continues there will almost certainly be an accident
High
Highly probable 5
Risk Priority Numbers aka. "RPN" Failure Detection Probability value
This value is based on the "ease" of detection of a failure. The number of Levels is 5, 1 = easy detection / failure is obvious, 5 = unlikely to detect before operational use or fails in service without warning.
i.e. n = 1 to 5.
1
Certain or Very High
Obvious failure - visually obvious, easy to notice, housing etc.)
2
High
Audio or visual alarm different Detection Probability value to the item which it is protecting)
3
Medium
Failure identified only by human monitoring / inspection extinguisher in red zone, engine oil levels)
4
Low
Failure apparent only through secondary indications. failure identified by rising CO2 levels)
5
Very low
Failure of emergency/backup system during operation or failure apparent only when it causes other systems fail (eg chamber flow fuse fails to operate after external pipework failure)
(e.g. not concealed within a
(Note: the alarm may have a
(eg gauge in fire
(eg scrubber
Use to the "Failure Detection Probability" value (n=1 to 5) calculate the Risk Priority Number "RPN" for an Item
RPN = Severity x Probability x Detection Probability the possible RPN range is 1 to 125 e.g. Severity = 4, Probability = 1 and the Detection Probability = 5 (i.e. very low chance of detection) RPN = 4 x 1 x 5 = 20. Notice the Risk Matrix score is 4 (Low Risk) nothing needs to be considered. But!...? Calculating an RPN can assist in decision making as to where remedial action needs to be concentrated first resources, Time, Manpower, Capital etc.)
(i.e. the most efficient allocation of
A high RPN ranking will also be an strong indication that changes are required to the SOP, PMS and critical spares compliment on the system.
Absolute Evaluation Method - Risk Index Work Sheet. Low
Severity Ratings: Numerical Value:
Negligable
1 No absence from work
Health and Safety: No significant impact. Easily controlled on worksite
Environment: -
Operations: -
Short or no delay in operations. Trivial asset damage
Low
Probability Ratings: Numerical Value:
Extremely Improbable
1 An accident could only occur under freak conditions
Failure Detection ' Probability Rating: Numerical Value: Note: 'This is an Ranking -
High
Certain
1 Obvious failure - visually
"Inverse" obvious, easy to notice, ' (e.g. not concealed within a Easy housing etc.) Detection Probability = 1 ' Very Low Detection Probability = 5
Risk Index Information: RI <= 2.250 is OK. Select value of nMax. Suggest nMax. = 5 or 10 Reject Solution, Situation Unacceptable / Do not Operate Do Not Use! / Suspend Pending Review / Advise Management Restrict Use, Operate with Extreme Caution if it is necessary to continue operations. Operate with Caution OK to Operate! Acceptable Solution OK! Acceptable for Operations: RI = < 1.000 is not a valid resul
n = 1 to 5
RI Value as % of nmax.
5.000 100.00%
2.875
62.50%
2.625
57.50%
2.375
52.50%
2.250
50.00%
1.750
40.00%
0.750
20.00%
1.000
0.00%
The Calculation of Risk Index (RI) Risk Index
Each element's score a, b and c is obtained from our understanding and expertise of the it transformed in to the new synthetic evaluation index RI, which is a numerical value indicat view point of control technology (and safety). The Optimal RI
If we accept the optimal score of each element is 50% of the Max Score of n = 5, then the exceed 2.5, the current control measures are considered to pass FMEA / FMECA assessmen evaluation smoothly.
a=2.5, b=2.5, c=2.5 Which of course will provide an RI of 2.500 which in this evaluation w Optimal RI value can be "tightened" up to a smaller number e.g. 2.000 or 2.250 if circumst
If operational requirements dictate a lower level of risk, the Optimal score can be recalcula Optimum Risk Index value. If this is done and we are using a range of n = 1 to 5, any calc between 2 and 5 requires further treatment, management or reengineering. Changing the Optimal RI % of the applied range will (of course) require
The Necessity for Special Index and Formula to include "Detectability Probability However, it is difficult for the case where the combination of a score is
a= 3, b= 3, c= 1 - Here we have 2 values which are relatively high and a low number, loo result is 18 which again is looking high, however taking the cubed root of the product we h Reducing our RI (Risk Index) back to a scale of n = 1 to 5 is considerably more manageable expertise and knowledge in the 3 areas we are considering to produce a viable and reliable
The following formula will be obtained when this problem is dealt with using control techno i.e. we are calculating the cube root of Probability x Severity x Detectio formula is written as RI = POWER( (S * P * DP),1/3) e.g. using cell refe
You can substitute the element scores into this expression and get a synthetic evaluation s The Reason for the Dimensional Return
The elements a, b, and c are one-dimensional values which show the necessity for measur the necessity for measures, the three-dimensional value needs to be returned to a one-dim (Probability x Severity x Detection Probability) as described above. Discussion of the Reason for the one-dimensional value
The calculation of RI should not make an arithmetic average but a cubic average. This is be Additionally, by performing this calculation (finding the cubed root of the product) the resu and context as the original values. i.e. n = 1 to 5 in our case Even if operational necessities dictated the requirement for n = 1 to 1 still remain in the context of n = 1 to 10 (if calculated as the cubed root of the product). A score (5) as the Optimal RI value. (An RI of 4 could also be considered if circumstances dic and need to be decided upon to fit the context in which they are being used, to create prac outcomes while at the same time being represented in a simple and intuitive fashion so as
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dex Work Sheet.
following the work of Takaro Unuma. OLT Institute, Japan Brief Discussion follows below!
Severity
Low
Slight
Moderate
2
3
High
Serious
Very serious
4
5
Minor first aid required
Injury leading to lost time
Possible permanent disability, possible fatality
Short term effect on site, controlled on worksite
Local pollution, may have lasting effect on worksite
Pollution extending beyond Major uncontrolled release worksite, effects for more extending beyond worksit than 6 months Serious pollution for > tha 12 months
Minor delay in operations. Minor asset damage.
Operation delayed/Degraded. Moderate asset damage.
Operational failure. Serious Operational failure. Critica asset damage. asset damage.
Probability
Low
High
Improbable
Possible
Probable
2
3
4
An accident might occur if other factors were present but the risk is minimal.
Highly Probable
5
An accident may occur if an The accident could easily If work continues there wi additional event takes be caused by environmental almost certainly be an place. conditions, platform accident instability, vibration or human carelessness.
Detectability
High
One or more fatalities
High
Medium
2
3
Audio or visual alarm Failure identified only by (Note: the human monitoring / alarm may have a different inspection Detection Failure Probability (e.g. gauge value to the item which it is in fire extinguisher in red protecting - This should also zone, engine oil levels) be considered)
Low
Low
Very Low
4
5
Failure apparent only Failure of a system or an through secondary emergency backup system indications. during operation with the (e.g. failure apparent only when scrubber failure identified by causes other systems fail rising CO2 levels) (e.g. chamber flow fuse fails to operate after external pipework failure)
Enter
Risk Index Calculator:
Risk Index Optimum as a % below
("Open" enter "P", "S" & "FDP")
Manual Entry ! where "RI" = (Prob x Severity x Det. Prob.)1/3
45.0% Range < = 5.000 & > Range 2.875 < = 2.875 & > Range 2.625 Range
< = 2.625 & > 2.375
Range
< = 2.375 & > 2.250
P
S
FDP
2
3
2.5
OK to Operate! Acceptable Solution
< = 2.250 & > Range 1.750 < = 1.750 & > 1.000
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Hyperlink to Systems & Sub-Systems:
following the work of Takaro Unuma. OLT Institute, Japan ref. http://www.geocities.jp/takaro_u/fmea_eng.html#c6-5
erstanding and expertise of the item of equipment or the process we are studying, these scores are which is a numerical value indicating the degree of lack (i.e., additional need) of control measures f
the Max Score of n = 5, then the Optimal RI is 2.5. When each element obtains the score which do to pass FMEA / FMECA assessment. For example, the failure mode that obtains the score shown bel
of 2.500 which in this evaluation we are considering to be optimal. ber e.g. 2.000 or 2.250 if circumstances required this.
he Optimal score can be recalculated to 40% (for example) of the Max Score of "n MAX", this will lowe ng a range of n = 1 to 5, any calculated RI between 1 and 2 will be considered to be acceptable an nt or reengineering. plied range will (of course) require recalculating of the "Risk Index Information" column as shown ab
lude "Detectability Probability" into the evaluation. n of a score is
atively high and a low number, looking at them makes subjective judgement difficult, multiplied toge he cubed root of the product we have a result of 2.080 which is < 2.5 and there for an acceptable v is considerably more manageable than working on a scale of n = 1 to 125 (5x5x5) and requires mu ng to produce a viable and reliable answer.
is dealt with using control technology. of Probability x Severity x Detection Probability. S * P * DP),1/3) e.g. using cell references "POWER((G21*H21*I21),1/3))" )
n and get a synthetic evaluation score, based on the next reasons.
ch show the necessity for measures. In order similarly for RI to serve as a one-dimensional value wh needs to be returned to a one-dimensional value. We achieve this by taking the Cubed Root of the ed above.
age but a cubic average. This is because each score a, b, and c have a mutually different meaning. ubed root of the product) the resulting answer remains a meaningful and practical number in the sa case ated the requirement for n = 1 to 10 for probability, Severity & Detectability, the resultant RI value w the cubed root of the product). Additionally, it would be practical to select the median value of eac be considered if circumstances dictated tightening up the criteria, remember all these values are su hey are being used, to create practical, efficient and economic solutions, which will produce optima simple and intuitive fashion so as not to confuse management.)
ref. http://www.geocities.jp/takaro_u/fmea_eng.html#c6-5
Enter Values
y serious
5
e or more fatalities
Selecte d
w!
SH&S = 3
or uncontrolled release ending beyond worksite. ious pollution for > than months
Risk Index Calculator:
where "RI" = (Prob x Severity x Det. Prob.)
P
S
FDP
3
2
3
SE =
2.3
erational failure. Critical et damage.
SO = 1
Operate with Caution
Risk Index Info Table:
hly Probable
5
ork continues there will ost certainly be an ident
P=
2
y Low
5
ure of a system or an ergency backup system ng operation with the ure apparent only when it ses other systems fail (e.g. mber flow fuse fails to rate after external ework failure)
FDP =
3
Risk Index Calculator: (Linked to and duplicating the calculator above)
x Det. Prob.)
1/3
where "RI" = (Prob x Severity x Det. Prob.)1/3
RI
P
S
FDP
RI
2.466
3
2
3
2.621
olution
g, these scores are control measures from the
Operate with Caution
he score which does not e score shown below passes The
", this will lower the o be acceptable and anything
MAX
olumn as shown above.
ult, multiplied together the or an acceptable value. 5) and requires much less
(the excel
mensional value which shows Cubed Root of the product of
ifferent meaning. l number in the same range
esultant RI value would then edian value of each max hese values are subjective ill produce optimal safety
g.html#c6-5
erity x Det. Prob.)1/3
RI
2.621
Caution
General Guidance: http://www.weibull.com/basics/fmea_fig1.htm
commonly used format: (conventional)
Use Top-down Analysis on already-known processes Use Bottom-up analysis for R&D, Product Development and Procedureal Design
sed format: (conventional)
Abbreviations ABS ASME AODC BIBS CO2 CO DDC RCL DESIGN ECU FMEA FMECA FSW HeO2 HP H2S HLB ID IMCA IOGP LARS LSP LR LP MSW Nitrox OD O2 P & ID PMS Sat. PVHO RPN SWL SPF SWR SDC TUP TUPC
American Bureau of Shipping American Society of Mechanical Engineers Association of Offshore Diving Contractors Built In Breathing System Carbon Dioxide Carbon Monoxide Deck Decompression Chamber Divers Reclaim Diving Equipment Systems Inspection Guidance Note (IMCA DESIGN) Environmental Control Unit Failure Modes and Effects Analysis Failure Modes and Effects Criticality Analysis Feet of Seawater Helium & Oxygen Mixed Gas High Pressure Hydrogen Sulphide Gas. Hyperbaric Life Boat Internal Diameter International Marne Contractors Association International Oil and Gas Producers Launch and Recovery System Life Support Package Lloyds Register Low Pressure Meters Sea Water Nitrogen & Oxygen Mixed Gas Outside Diameter Oxygen Piping and Instrumentation Diagram Planned Maintenance System Prefix used for Saturation Pressure Vessel for Human Occupancy Risk Priority Number (Probability x Severity x Detection Probability (before failure)) Safe Working Load Single Point Failure Steel Wire Rope Submersible Decompression Chamber aka. Diving Bell Transfer Under Pressure Transfer Under Pressure Chamber.
